A variety of non-linear structures exhibit negative mechanical stiffness, such as snap-through beams and buckling beams. Negative stiffness may also be exhibited by various combinations and arrangements of springs and/or beams with pinned or clamped boundaries. For instance, negative stiffness may be exhibited due to over-rotation of one of the components, or rolling or sliding contact between components. Negative stiffness mechanisms are useful in a variety of applications, including vibration isolation, shock mitigation, and signal processing.
Additionally, many related art negative stiffness mechanisms achieve high isolation travel and nearly linear negative stiffness by using a higher-order mode buckled beam. However, the use of a higher-order mode buckled beam limits the ability to change the negative stiffness (which is possible with first-order beam bending) and limits the ability to create a widely adjustable positive spring component. For instance, when beams are buckled they exhibit high negative stiffness, and when beams are unbuckled they exhibit positive stiffness. Due to the nature of higher-mode buckling, however, the negative stiffness is generally independent of the amount of beam compression, and therefore conventional negative stiffness mechanisms are limited to at most two states (i.e., many related art negative stiffness mechanisms are switchable between only two negative stiffness states, on and off). To put it another way, many related art negative stiffness mechanisms are not configured to switch or change between multiple negative stiffness states. In contrast, a device incorporating beams configured to switch between multiple states would allow the device to exhibit multiple values of negative stiffness because the full device stiffness is the sum of all beams.